Pipe, standard input and command line arguments in Bash

Question

Consider:

command1 | command2

Is the output of command1 used as standard input of command2 or as command line arguments to command2?

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Answer 1

Another form of redirection is process substitution.

grep "hehe" <(cat test.sh)

is equivalent to:

grep "hehe" test.sh

which both look at the contents of test.sh itself.

While, as it has been noted, this command:

grep "hehe" $(cat test.sh)

looks for filenames in test.sh and uses them as arguments for grep. So if test.sh consists of:

scriptone
scripttwo

then grep is going to look for "hehe" in the contents of each of those files.